People snapped selfies with Rosa Parks’s mug shot and studied artifacts like Harriet Tubman’s shawl. They lingered over verses by Langston Hughes and Maya Angelou inscribed on the walls. They read out text about the literal prices paid for families torn apart by slavery, tracing and celebrating their own complicated lineage.

“We are now able to have ourselves be defined by our selves,” said Sandra Taylor, 51, a business consultant from New Bern, N.C. “I’ve been elated, I’ve been proud. Informed is not an emotion, but I have just been inspired by so many stories.”

The museum’s arrival in the last months of the Obama administration, as the nation grapples anew with racial inequality, resonated with many. “The timing is prophetic — you can’t visit here and not think about what’s going on today, and the sense of history and struggle,” said Bishop Paul L. Walker, 51, a pastor from Rockville, Md.

The museum, part of the Smithsonian Institution, sits on a coveted spot on the National Mall, and turned its opening into a three-day celebration, with a dedication by President Obama on Saturday, and a free music festival. Many attendees on Sunday wore buttons from the dedication ceremony, proclaiming “I was there!”

Timed, free tickets for entry were snapped up months in advance: Ms. Taylor used three devices to secure them the day they were offered, in August.

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Florence Claggett, a retired federal worker who watched the museum building rise in Washington.CreditJustin T. Gellerson for The New York Times

Over the weekend, entrance lines snaked up along the Mall. On Sunday, opening hours stretched from 7 a.m. to midnight. The building was packed throughout.

Still, the mood was largely jubilant. “The crowds, that’s part of the excitement,” Ms. Taylor said.

Decades in the making after a hard-fought Congressional battle for funding, the museum felt to many like a culmination. “It has brought everything together,” said Florence Claggett, 66, a retired federal employee, who has tracked its progress for years, sometimes from her office window across the street.

Ms. Claggett had attended the March on Washington in 1963.

“I was 13 years old,” she said. “I rode the bus all the way down Seventh Street; I was at the end of the reflecting pool.” She said the museum gave her “a sense of accomplishment, where we stand on the backs and shoulders of all the people who came before us.”

On Sunday afternoon, a choir from Morgan State University, the largest historically black college in Maryland, sang spirituals and “Glory,” the Oscar-winning song from the movie “Selma.”

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Visitors waiting in line to see the coffin of Emmett Till.CreditJustin T. Gellerson for The New York Times

“It was definitely a life-changing experience, being here, to see a tangible representation of our history in American history,” said Ayanna Freelon, 21, a choir member. “If our accomplishments were incorporated into everyday education, I feel like that would ease the tension of race relations. People don’t understand our culture.”

Teachers and staff members from a Washington middle school took photos in preparation for a visit by their students later this week. “Some of these numbers really set in my head,” said Dhakkiyyah Lee, 30, as she studied a display that recounted how slaves routinely died during the ocean crossing. In 1730, a French ship carrying 170 slaves arrived with only one survivor.

“You just have to face the reality,” Ms. Lee said, after passing through a darkened, hushed room that included a pair of child-size shackles. “It was brutal. And it should not be sugarcoated.”

People came primed for emotionally wrenching presentations. “What’s depressing is not so much that it happened, but that it’s still happening,” a woman said, as she stood by the coffin of Emmett Till, the 14-year-old viciously murdered by white men in Mississippi in 1955.

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Lisa Walker and her husband, Bishop Paul L. Walker; each of their families donated artifacts to the museum.CreditJustin T. Gellerson for The New York Times

In the consolation room, a quiet, artifact-free spot in the center of the building, where an orb of rain continuously falls from the ceiling, Marie Scruggs and her family were brought to tears. Ms. Scruggs, 80, a retired educator from Missouri, came with her son and daughter-in-law, partly to memorialize her husband, Donald. Both had been active in the civil rights movement. “Fairness, justice, equality,” Ms. Scruggs, who is white, said, about what motivated them to join the demonstrations.

On the museum’s top floors, at exhibitions dedicated to culture, community and sports, people danced to Tina Turner videos and hummed Donna Summer disco hits. But the specter of this year’s polarizing election was never far off. “Black Girls Vote” read one woman’s T-shirt. Black Lives Matter shirts were also common.

“It’s disheartening,” said Keena Lewis, 31, who works in acquisitions for the Department of Homeland Security, “because it’s the same fight that has been fought for 400 years. And it’s just that I want to be treated equally.”

Bishop Walker said that for all the bleak truth on view, the museum gave him the sense of a culture and a people moving, relentlessly, forward. “Things are still progressing,” he said, a sentiment echoed by many visitors.

Kola Anjou, 67, a retired business owner, had a similar thought. “What makes America great is that there are people who rise up and make corrections, up to the present day,” he said. “America has a conscience. That’s what keeps it still rising. That’s what makes it great.”

A version of this article appears in print on , on Page C2 of the New York edition with the headline: On a Museum’s Crowded Opening Day, a Sense of Pain and Pride. Order Reprints | Today’s Paper | Subscribe